Decongestants are commonly used to relieve nasal congestion and a commonly used decongestant is phenylephrine. Phenylephrine is widely available to consumers as an over-the-counter (OTC) drug.
One problem for immediate release dosage forms containing phenylephrine is that in order for it to be most effective, it must be taken frequently. The current U.S. Monograph for an oral dosage form comprising phenylephrine hydrochloride is ten milligrams every four hours. Consumers find it inconvenient to dose every four hours and frequently miss doses, especially mid-day doses, which can result in poor symptomatic relief.
Furthermore, the short time period between doses makes it difficult to combine phenylephrine with other drug actives, in particular actives that are commonly used in multi-symptom relief cold/flu products, which have longer dosing intervals. Therefore, consumers have to take multiple dosage forms and dose several times a day at various intervals to experience the optimal relief of their cold/flu symptoms.
One of the reasons for frequent dosing is because phenylephrine is subject to high first pass metabolism and a short half-life. Upon oral administration, phenylephrine is rapidly metabolized and is subsequently conjugated into sulfate and glucuronide forms. However, the therapeutic decongestant activity is attributed to the portion of the phenylephrine that is not metabolized and stays as the unconjugated parent active. Accordingly, it is of benefit to maximize the duration of time of the unconjugated active form present in bloodstream after oral administration.
There have been several attempts to modify the release of phenylephrine in order to prolong the dosing interval. Many approaches related to the modified release of phenylephrine focus on dual release mechanisms comprising an immediate release form coupled with an extended first-order or zero-order extended phase of release. A problem with these bi-modal approaches is that during the extended release phase, low levels of unconjugated phenylephrine active are likely to be present in the bloodstream due to rapid first pass metabolism. An alternate approach would be a pulsatile dose form that releases active at different regions in the intestine and can mimic immediate release dosage forms administered every 4 hours. Such a dosage form would be beneficial to the consumer and allow for more effective and convenient dosing.
As such, there remains a need in the area of consumer selected OTC therapies for improved options for the treatment of symptoms associated with the common cold (rhinovirus), influenza, or environmental allergies. In particular, there exists a need for a convenient longer acting phenylephrine dosage form that can provide relief over an extended period of time relative to current therapies.